Induction cooking/warming appliance including vessel supporting means having an undulant surface and temperature sensing means associated with said surface

ABSTRACT

Disclosed herein is an induction range having a counter including an undulant top surface for supporting a cooking vessel. Since the counter is made of a material which is not inductively heatable the counter remains relatively cool during the cooking process, while the vessel is being inductively heated. Although the counter&#39;&#39;s top surface has undulations therein, it is, nevertheless, an unbroken surface; i.e., there are no openings therethrough. Moreover, even though the counter&#39;&#39;s top surface has undulations therein, it may, nevertheless, be relatively smooth so that it can be wiped clean, easily. Furthermore, temperature sensing means are arranged on the top surface of the counter between adjacent undulations thereof and said sensing means are adapted to be contacted and easily compressed by the bottom surface of a vessel resting on the counter&#39;&#39;s top surface; i.e., resting on the undulations.

United States 91 Harnden, Jr. et al.

[ 51 Eeb.6,1973

[75] Inventors: John D Harnden, Jr., Schenectady, N.Y.; William P.Kornrumpf, Schenectady, NY.

[73] Assignee: General Electric Company [21] Appl. No.: 228,135

[52] US. Cl ..2l9/10.49, 73/343 R, 73/351, 126/39 J, 219/10.75, 219/504[51] Int. Cl. ..ll-l05b 9/00 [58] Field of Search.....219/10.49, 10.77,10.79, 502, 219/504, 10.75; 126/39 J; 73/343 R, 351, 362 AR; 340/210,210. MB;'307/117 OTHER PUBLICATIONS Murakami, Characteristics of FerriteCores with Low Curie Temperature, IEEE Trans. on Magnetics, June, 1965,pp. 96-100.

Primary Examiner-R. F. Staubly Assistant ExaminerB. A. ReynoldsAtt0rney-J0hn F. Ahern et a1.

[57] ABSTRACT Disclosed herein is an induction range having a counterincluding an undulant top surface for supporting a cooking vessel. Sincethe counter is made of a material which is not inductively heatable thecounter remains relatively cool during the cooking process, while thevessel is being inductively heated. Although the counters top surfacehas undulations therein, it is, nevertheless, an unbroken surface; i.e.,there are no openings therethrough. Moreover, even though the counterstop surface has undulations therein, it may, nevertheless, be relativelysmooth so that it can be wiped clean, easily. Furthermore, temperaturesensing means are arranged on the top surface of the counter betweenadjacent undulations thereof and said sensing means are adapted to becontacted and easily compressed by the bottom surface of a vesselresting on the counters top surface; i.e., resting on the undulatrons.

17 Claims, 7 Drawing Figures PATENTED F 5 I973 SHEET 10F 3 4 M 2\\|\|.I| llllllx 4 0 A 0 4 MM 4 5 MW pm hm, H. 0 MW. 6 3 V0 nn 4 m H 6 3w m 4 1 MM M A 2 J 2 3 0A l mu ow 6 a W M 6 n, U N A MWW M mwfi m M Z a0 3 H PATENTEDFEB 6 ma SHEET 3 BF 3 TZMPLWATl/R' W INDUCTIONCOOKING/WARMING APPLIANCE INCLUDING VESSEL SUPPORTING MEANS HAVING ANUNDULANT SURFACE AND TEMPERATURE SENSING MEANS ASSOCIATED WITH SAIDSURFACE CROSS-REFERENCES TO RELATEDv APPLICATIONS A fuller appreciationof induction cooking appliances, as well as some of the sophisticationswhich may be embodied therein, is to be had by referring to thefollowing U.S. Pat. applications: Ser. No. 200,526, filed 11/19/71, inbehalf of David L. Bowers, et al., titled Solid State Induction CookingAppliance (RD-4675); Ser. No. 200,424,.filed 1 1/19/71, in behalf of J.D. Harnden, Jr. et al., titled Solid State Induction Cooking AppliancesAnd Circuits (RD4678). The entire right, title and interest in and tothe inventions described in the aforesaid patent applications, as wellas in and to the aforesaid applications, and the entire right, title andinterest in and to the invention herein disclosed, as well as in and tothe patent application of which this specification is a part, areassigned to the same assignee.

BACKGROUND OF THE INVENTION The invention herein disclosed pertains, ingeneral, to induction cooking/warming appliances; and, in particular, toan induction cooking/warming appliance having a vessel supporting means,such as a counter, which is provided with an undulant surface which isadapted for supporting a cooking/warming vessel and for receivingbetween its undulations temperature sensing means which are adapted tobe contacted and easily compressed by a vessel supported on the undulantsurface. An important feature of the aforesaid vessel supporting meansis that even though it is provided with undulations, it is,nevertheless, relatively smooth and, as a result, may be easily wipedclean. In addition to being undulant and relatively smooth, the surfaceneed have no apertures therethrough so that the surface may be used forfood preparation (e.g., cutting, chopping, grating, etc.). Furthermore,since the vessel supporting means is not made of inductively heatablematerial, the vessel supporting means and its surface remain relativelycool. Thus, easy cleaning and food preparation are facilitated, evenduring the cooking process.

Certain desiderata with respect to cooking/warming appliances have cometo the attention of the manufacble in thekitchen. Another advantage ofproviding a cool counter, or cook surface, is that there becomesavailable a wider choice of materials from which the counter, or cooksurface, may be fabricated. Elevated temperatures are not a restriction.

Two, the surface of the aforementioned counter or cook surface should berelatively smooth and unbroken (no apertures therethrough), as well asrelatively cool, so that it can be easily wiped clean with minimumeffort after food has been spilled (and contained) thereon.

Three, accurate sensing and display of cooking temperatures, and ofrates of temperature rise and fall, should be provided with suchappliances.

Prior art electric and gas ranges do not enable achievement of theaforementioned desiderata. Conventional prior art electric ranges employexposed sheathed resistance heater surface elements which areincorporated in the plane of the counter, or cook surface, and theseheater elements are electrically energized so that they can glow toincandescence. Conventional prior art gas ranges employ open flameswhich emanate from gas manifolds, or burners, which are incorporated inthe counter or cook surface. Thus, because of the nature of the primaryheat source and its arrangement and proximity with respect to thecounter, or cooking surface, temperatures of approximately 1,600 F mayoccur at or near the cook surface in such prior art cooking ranges.Manifestly, the counter or cook surface in such ranges do not operate ata relatively cool temperature; i.e., near ambient room temperature. Inaddition to being subjected to elevated temperatures the counter, orcook surface, of such prior art ranges must necessarily be constructedto accommodate resistance heater elements or gas manifolds and nozzles.Hence, such prior art ranges are provided with counters or cookingsurfaces which are irregular, unsmooth and broken (apertured).Therefore, food spilled on such counters or cooking surfaces often burnsand chars; The result is that extraordinary efforts, such as scouring,must be undertaken in order to clean up after such food spills. Ofcourse, such tasks are not made easier because ofthe irregular, unsmoothand broken construction of the counter or cooking surface.

Also, another type of electric range (the glass-ceramic electric range)has recently appeared wherein electrical resistance heater elements, orstrips, are embedded in a thermally conductive glass-ceramic counter, orcooktop. The counter, or cooktop as it is sometimes called, has a verysmooth top surface and the glass-ceramic material from which it is madeconducts heat very well. Since the counter, or cooktop, is provided witha very smooth (optically flat) top surface special cooking utensils, orvessels, are recommended for use in conjunction with such a counter orcooktop. The special cooking utensils, or vessels, have a very smooth,optically flat bottom surface so that when rested on the cooktop orcounter they are said to be mated with the cooktop. Briefly, because ofthe aforesaid mating of the optically flat utensil with the opticallyflat cooktop of the glass-ceramic counter, heat transfer from theembedded resistance heater elements is almost exclusively by means ofconduction; i.e., heat is conducted from the resistance heater elements,through the counter and directly into the utensil. With such an electricrange the cooktop is temperature restricted in that it cannot, withoutdestruction, withstand temperatures higher than 600 C (1,1 12 F).Moreover, if the temperature of the glassceramic cookstop cooktop toohigh electrical leakage current from the embedded resistance elementsbecomes of concern and represents a design restraint. Also, theglass-ceramic cooktop represents a relatively large thermal mass and thecooktop does not readily dissipate its stored heat after termination ofthe cooking operation, i.e., after the resistance heater elements aredeenergized it takes a relatively long period of time for the cooktop tocool down to normal room temperature. Thus, in commercially practicalembodiments of the aforementioned electric range employing theglassceramic cooktop, or counter, a reliable temperature control systemis at least required for the important purpose of preventing destructionof the cooktop due to elevated temperatures. Thus, the cooktop, orcounter, can be considered to be the primary heat source in theglass-ceramic electric range; i.e., the glass-ceramic. counter, orcooktop, is the primary heat source and is the equivalent of thespirally wound electrical surface heaters in the conventional electricrange, or equivalent to the gas flames in the conventional gas range.

Thus, the glass-ceramic electric range fails to fulfill the desideratahereinbefore set forth: a) The counter or cooktop certainly does notremain relatively cool during the cooking process because of the natureof the cooking process; i.e., heat transfer occurs by conduction throughthe counter, or cooktop, to the special utensil, or vessel, which ismated with the cooktop. b) Although the cooktop, or counter, has asmooth surface, food spilled thereon tends to burn or char. As a result,it cannot be said that it can be easily wiped clean. c) Although thecooktop or the surface of the counter is smooth, parts of the cooktopcannot be used for the food preparation operations hereinbefore setforth because of the excessive heat in the cooktop during and after thecooking operation.

With respect to sensing or detecting the true temperature of a cookingvessel or utensil resting on the range counter or cook surface theconventional prior art electric and gas ranges present a number ofproblems:

First, in prior art electric and gas ranges a temperature sensor unitand its associated components are spuriously heated in some measure bythe primary high temperature heating source. In the conventionalelectric range, for example, a temperature sensor unit is located at thecenter of a spirally wound resistance heating coil. This heating coil iselectrically energized and often glows to incandescence. The heating oiland temperature sensor unit are both located on the top surface of therange counter or cook surface and a cooking vessel or utensil rests uponand contacts the spiral heating coil as well as the temperature sensorunit. Although the temperature sensor unit directly contacts and sensedthe temperature of the heated cooking vessel the sensor unit is alsosubjected to direct spurious heating by the heating coil; e.g., byradiation and convection. In addition, the temperature of the sensorunit is influenced by, among other things, a metallic counter top withwhich the electric range is provided. Similarly, in prior art gas rangesthe open flames directly heat the temperature sensor unit and heatedmetallic gridirons, as well as a metallic counter top, thermallyinfluence the temperature sensor unit. In brief, with prior art electricand gas ranges the primary heating source spuriously heats thetemperature sensor unit and other heated parts of the range alsothermally perturb the temperature sensor unit. Such perturbations tendto frustrate the achievement of accurate temperature measurement.

Second, in prior art electric and gas ranges various component parts ofthe temperature sensing unit have to be fabricated from materials whichare capable of withstanding relatively high temperatures; e.g., up toabout l,600 F, approximately. As a result, certain materials cannot beused. For example, in the conventional electric range wherein thetemperature sensing unit is located at the center of the spirally woundresistance heating coil (which is mounted on the metallic counter top ofthe range) the temperature sensing unit and its associated componentsare subjected to maximum temperatures of approximately l,600 F andsignificant thermal stresses are induced in the temperature sensor unitand its associated components. In addition, the metallic counter isthermally stressed. Clearly, epoxies, plastics and polyimides, amongothers, are not applicable for use. Similarly, elevated temperatures andconsequent severe thermal stresses are present in gas ranges and manymaterials including those hereinbefore set forth are not applicable foruse. In brief, because of the relatively high temperatures involved inprior art electric and gas ranges, the materials from which temperaturesensing units including their associated components may be fabricatedare quite restricted.

Third, in prior art electric and gas ranges the temperature sensing unitand its associated components are often required to have some thermalshielding, or insulation, to minimize the influences of spurious heatingthereof by the high temperature heating source as well as by the'heatedmetallic range counter and the heated gridirons. Without some effectivethermal shielding or insulation, the temperature sensing unit willprovide a completely false temperature indication, unless temperaturecompensation is appropriately applied. However, temperature compensationis not feasible over the wide range of cooking conditions. Moreover,without effective thermal shielding severe thermal stresses induced inthe various components of the temperature sensing unit will cause adisabling or destruction of the temperature sensing unit. Briefly,because of the relatively high temperatures involved in prior artelectric and gas ranges, the temperature sensing units employed thereinrequire effective thermal shielding or insulation.

Fourth, prior art temperature sensing units, especially those employedin the conventional electric range, are rather sophisticated,mechanically, and are of a somewhat complex structure and arrangement.The high temperature environment within which the temperature sensingunit is located permits severe thermal stresses to occur in variouscomponents of the temperature sensing unit. These stresses tend topromote warping of the various components. For example, because of theaforesaid severe thermal stresses a relatively massive double springarrangement is employed in combination with a temperature responsivedevice. The temperature responsive device, acting against springrestraint, contacts the bottom surface of a cooking vessel which isseated on a flat spiral resistance heating coil and on the temperatureresponsive device, both of which are located on the top surface of themetallic range counter. The massive double spring arrangement is ratherstiff (i.e., the spring has a relatively high restoring force or arelatively large effective spring constant) due, in large part, to theneed to make the arrangement structurally resistant to serious thermaldeformation. Such a stiff spring arrangement generally functionssatisfactorily to maintain the temperature sensing unit in contact withthe more or less regular flat bottom surface of a relatively heavyvessel, such as a cast iron pot, containing foodstuff tobe cooked. Sinceit is in contact with the bottom surface of the vessel, or pot, it isconceptually possible for the temperature sensing unit to detect thetemperature of the vessel. However, in the event that a relatively lightpot, or vessel, is used or if the foodstuff contained therein is not ofsufficient weight, such prior art temperature sensing units employingthe aforesaid stiff spring arrangement prove unsatisfactory. Such anarrangement is also unsatisfactory where the vessel has an irregularlycontoured bottom surface. For example, if a relatively light cookingvessel is employed, there will be insufficient vessel weight toadequately compress the spring arrangement and one consequence will bethat the vessel will not rest on the resistance heating coil in the mostintimate contact possible therewith, i.e., the vessel will be raised, ortilted, and thereby cause inefficient heat transfer between theresistance heating coil and the vessel. Suffice it to say that: becauseof the relatively high'temperatures involved and because of theconsequent severe thermal stresses created it is not practical toprovide temperature sensing units having simple spring arrangements withrelatively low effective spring constants; i.e., little spring stiffnessor relatively small restoring force. 7

Also, the so-called glass-ceramic type of electric range, hereinbeforedescribed, would appear to present many of the same problems withrespect to sensing, or detecting, the true temperature of thecooking'vessel, or utensil, resting on the glass-ceramic cooktop as arepresented with the conventional prior art electric and gas ranges:

First, inasmuch as the glass-ceramic cooktop, or counter, containing theembedded electrical resistance elements is, in effect, the primaryheating source in such a range, a temperature sensing unit so disposedor arranged as to contact the cooking vessel for the purpose ofdetermining the temperature thereof would tend to be spuriously heatedin some measure by the elevated temperature of the glass-ceramiccooktop. Thus, the glass-ceramic type of electric range appears topresent the same kinds of problems in this respect as tures involved inthe glass-ceramic type of electric range, the materials from whichtemperature sensors and their associated components may be fabricatedwould be quite restricted.

Third, in attempting to determine the temperature of a cooking vessel, atemperature sensing unit and its associated components employed inconjunction with the aforesaid glass-ceramic type of electric rangewould have to be thermally shielded or insulated, effectively. In brief,most of the same problems encountered with conventional prior artelectric and gas ranges would also be encountered with the glass-ceramictype of electric range where effective thermal insulation or shieldingis concerned.

Fourth, prior art temperature sensing units employing rathersophisticated and complex structures or arrangements of massive doublesprings might be employed in conjunction with the glass-ceramic type ofelectric range. However, it appears that a suitable aperture orapertures would have to be provided through the glass-ceramic cooktopsurface. In any event, the same problems as hereinbefore discussed withreference to the conventional prior art electric and gas ranges wouldappear.

SUMMARY OF THE INVENTION Although the invention is hereinafterdescribed, and illustrated in the accompanying drawing figures, as beingembodied in an induction range, it is, nevertheless, to be understoodthat the applicability of the invention is not limited to inductionranges but may be embodied in, for example, trivet warmers, portablewarming or cooking appliances, as well as in other apparatus which neednot, necessarily, .be used for cooking food.

One object of the invention is to provide a cooking/warming appliancewhich includes a vessel supporting means, such as a counter or cooktop,having an unbroken, or non-apertured, top or working surface whichremains relatively cool during the cooking or warming process.

Another object of the invention is to provide a cooking/warmingappliance which includes a vessel supporting means, such as a counter orcooktop, having an undulated but unbroken or uninterrupted (i.e.,without apertures) top or working surface which remains relatively coolduring the cooking or warming process; although the top or workingsurface of the counter has undulations therein, it may, nevertheless, bewiped clean, easily.

Another object of the invention is to provide a cooking/warmingappliance which includes a vessel supporting means, such as a counter,or cooktop, having a undulant surface for supporting a cooking/warmingvessel or utensil and having between its undulations temperature sensingmeans for sensing the temperature of said vessel or utensil.

Another object of the invention is to provide a cooking/warmingappliance having a temperature sensing unit including a temperaturesensor unit and associated components or elements which are free fromspurious heating.

Another object of the invention is the provision of a cooking/warmingappliance having a temperature sensing unit including a temperaturesensor unit and associated components or elements which may beAnotherobject of the I was: .1 I Another object. of the invention is toprovide a cooking/warming appliance includinga temperature sensing ingmeans'.

,j IAn the'r object offthe invention is to provide anovel fabricatedfrom materials which are not usable in the relatively high temperatureenvironments created in the prior art electric, glass-ceramic and gasranges hereinbefore discussed.

extent,'employed in 'the prior art appliances hereinbefore discussed.

Another object of the invention is to provide a cool;-

ing/warming appliance having a temperature sensing unit including, inaddition to atemperature sensor unit, components orelements associatedwith said sensor unit which'provide a relatively small spring force(i.e., a relatively low restoring force or relatively low effectivespring constant) for maintaining the sensor unit in contactwith thesurface of a cooking/warming vessel or utensil. The vessel or utensilmay bev of relatively light weight 'and' may, in addition,have'a ratherirregularly contoured surface presented for contact with the temperaturesensor unit.- I c I invention is to provide a cooking/warming applianceincluding a temperature sensing unit for accurately sensing or detectingthe true temperature of a vessel orutensil being heated; said .tem-

perature sensing unit being capable of accurately sensing or;detecting'the temperature of the vessel regardless of the weight. ofthe-vessel or weight of the food'co'ntained therein; and/or-regardlessof whether the vessel has or has not an irregular surface or conunitwhich does not. require the'prior art spring constr uction'orarrangement hereinbefore discussed.

Anotherobject of the invention is to provide a cooking/warmingappliancel'wherein a temperature sensor unit positioned-betweenundulations in the surface of a vessel supporting means is instrumentalin enabling data representing "the ,temperature of the vesselsupportedon said surface to be magnetically coupled jithroughitheunbroken or uninterrupted vesselsupporttemperature sensor unitwhereinfthe magneticpermeability of saidun'it'is a function oftemperature.

"The aforementioned objects, as well as-other's, are

' achieved in accordance withone embodiment of the invention, towitzlaninduction cooking/warming ap-' ,pliance, for. heating a vesselhaving'at least one portion thereof inwhich heatingj cu'rrents may beinduced, comprising; support means in which no substantial heatingcurrent is induced when saidsupport means is I subjected'to a changingmagnetic field, said support means' having at least one surfaceincluding at least two spaced-apart undulations therein which define avalley portion on said one, surface between said two undulations,thevessel being supportable onsaid support means such. that said vesselrests on said two spacedapart. undulations; an induction coilenergizablefor producinga changing magnetic field in said one portion of the.vessel whensaid vessel is supported on said support means; means forenergizing said induction coil;

temperature sensing means disposed in said valley portion between saidundulations for sensing the temperature of the supported vessel 'and forproviding a-first signal representative of the temperature of thevessel; and, temperature receiving means, magnetically coupled with saidtemperature sensing means and said first signal, for providing a secondsignal representative of the temperature of said vessel.

One feature of the invention resides in the use of a vessel supportingmeans including a surface having undulations therein; the support meansbeing fabricated from a material or materials which will not permitheating currents to be induced therein. Thus, the support means remainsrelatively cool evenduring the cooking process. Thus spilled foods willnot burn, char or adhere to the support means. Furthermore, the supportmeans may be fabricated from a material or materials which need notwithstand temperatures beyond 550 F. Another feature of theinventionresides in the provision of a vessel support means which isrelatively smooth and capable of being wiped clean, easily, even thoughundulations are formed infthe surface of said support means.

Another feature of the invention resides in the em ployment of atemperature sensing unit in combination with the aforesaid undulatedvessel support means; e.g., the disposition and arrangement of avessel-contacting spring means, supporting a temperature sensor unit,between undulations in the aforesaid valley portion of the supportmeans.

Another feature of the invention residesin the use of a temperaturesensor unit which changes its electrical impedance, or resistance, as afunction of its temperature and using such temperature-correlatedimpedance or resistance changes in such a way that they are reflectedmagnetically, without the intervention of tangible physical means; to arelatively remote temperature receiving unit proximate the'vesselsupport means whereat signals representative of the temperature sensedor detected by said sensor unit may be utilized.

' Another feature of the invention residesin the employment of a noveltemperature sensing unitwherein a plastic .magnetic member includingtemperature responsive-material has .its magnetic permeabilityDESCRIPTION OF THE DRAWING FIGURES FIG. 1 is a perspective view of anupper part of an induction cooking range illustrating, among otherthings, a vessel support means, such as a rangecounter or cooktop,having undulations therein and temperature sensing means arrangedbetween some of the undulations.

' FIG. 2 is an enlarged cross section view, taken along I the sectionline 2-2 in FIG. 1, and showing, among other things, the inductionranges undulant counter and temperature sensing means as well as a blockdiagram of the electric power and temperature signal systems employedwith the subject invention.

FIG. 3is another enlarged cross section view shown in FIG. .2 butshowing, however, a fry pan supported on the undulant range counter andcontacting the temperature sensing means thereon.

FIG. 4 is a fragmentary plan view showing the temperature sensing meansdisposed on the surface of the range counter between adjacentundulations therein.

FIG. 5 is a greatly enlarged cross section view similar to the crosssection view shown in FIG. 2 but illustrating in more detail thetemperature sensing means and temperature receiving means employed inthe subject invention.

FIG. 6 is an enlarged cross section view similar to that shown in FIG. 5but showing an alternate temperature sensing means disposed betweenadjacent undulations in the top surface of the range counter.

FIG. 7 is a graph showing the variation of the magnetic permeability ofthe temperature sensing means of I FIG. 6 as a function of temperature.

DESCRIPTION OF PREFERRED EMBODIMENTS Shownin FIG. 1 is an inductioncooking range which The range 20 is provided with a counter 22, orvessel being dial-type thermometers. However, indicators may be digitaldisplays. On the top or working surface of the counter 22 there isillustrated four symmetrically arranged temperature sensing means, eachof which is designated generally by the reference number 32. At each ofthe temperature sensing means 32 a cooking vessel-or utensil (e.g'.,pot, pan, etc.) may be positioned for cooking It is contemplated thatthe vessel or utensil 'will be placed over the temperature sensingmeans, as suggested in FIG. 3, so that the temperaturesensing means 32is under the bottomsurface of the vessel or utensil at the approximatecenter thereof.

As indicated in FIGS. 1 and 2, there is associated with each'cookingposition on the range counter 22 the following, among other things: atemperature sensing means 32, a control 28, a temperature indicator 30and an induction'coil 40.

Situated beneath the counter 22 and separated therefrom by an air gap isa flat spirally wound induction coil'40. As shown, the coil 40 includesat the center thereof, an air core. As shown in FIG. 2, the inductioncoil 40 is electrically coupled to the output of a solid state inverter44 which, in turn, has an input which is electrically coupled to theoutput of a rectifier 46. The inverter 44 as combined with rectifier 46forms a static power conversion circuit designated, generally, bythereference number 43. The rectifier 46 includes an input whichiselectrically coupled to a conventional A.C. source 50; a 60 Hz, singlephase, l 10 or 220 volt tion coil 40. In brief, the control 28 ispreferably marked in degree F settings to enable the housewife, forexample to call for a certain temperature, or temperature range,performance. However, it is the temperature indicator 30 associated withthe particular control 28 which provides her with a visible indicationof the actual temperature of the vessel 38 or utensil (FIG. 3) as wellas of the rate of temperature rise and fall.

As for the conversion circuit 43, the rectifier 46 may be a regulatedfull-wave rectifier employing solid state devices and operating toconvert an A.C. input to a D.C. output and the inverter 44 preferablyemploys SCRs which, in the performance of their control switchingfunction, enable the inverter 44 to deliver a relatively high frequency(i.e., ultrasonic or higher) output to drive the induction coil 40. Thecontrols 28 and the temperature indicators 30 provide the actuation andvisible feedback functions hereinbefore described.

Also shown in FIG. 2 is a temperature signal processing circuit 52 whichincludes: a first input coupled to the rectifier 46 and derivingtherefrom a source of D.C. voltage; a second input in the form of a pairof electrical conductors extending from a magnetic receiving means 60 tothe temperature signal processing circuit 52; and, an output directlycoupled to a temperature indicator 30. The temperature indicator 30 maybe a dial-type thermometer suitably graduated in degrees F or in degreeranges or bands.

As illustrated in FIGS. 1 through 5 the temperature sensing means 32 iscomprised of: a relatively thin elastomeric cup-like member 33 such as,for example, a silicone rubber cup; a thermistor unit 34 partiallyembedded in and supported by the cup-like member 33; a magnetic couplingmeans 35 including a magnetic core 36about which there is wound acoil 37and a cylinder 39 within which thecore 36 and coil 37 are embedded orpotted. A pair of conductors 41 electrically couple the coil 37 with thethermistor unit 34.

In FIG. 3 the vessel 38 is illustrated as being filled with a food whichis to be cooked or heated; e.g., hamburgers. The vessel 38 is aconventional pan which may be made of cast iron, magnetic stainlesssteel, etc.; i.e.,

may be considered to be a specification temperature in that the vessel38 will not actually reach a temperature quite that high but when asafety factor is included 550 F is considered to be a nominalspecification temperature. As a result, the counter 22 may be fabricatedfrom materials which are not employable in the conventional prior artelectric or gas ranges; nor in the glass-ceramic electric rangehereinbefore discussed. For example, the counter 22 may be fabricatedfrom epoxies, plastics, polyimides, etc. If required for purposes ofelectrostatic shielding and/or structural enhancement and/or decorationthe counter 22 may include some metallic content. However, the inclusionof metallic material is necessarily limited to a small amount in orderto enable substantially all of the power developed by the induction coil40 to be coupled electromagnetically with the cooking vessel 38. In anycase, the amount of metallic material included should be so distributedas to prevent the formation of ohmic electrical circuits which wouldallow significant circulating-currents to be induced in the counter 22.In the alternative, the counter 22 may, if desired, be made of a glasswhich is suitably treated so as to withstand temperatures of 550 F. Asanother alternative, quartz may be employed in the fabrication of thecounter 22. Advantageously, as shown in the drawing figures, the counter22 presents an uninterrupted or unapertured working or top surface.

As illustrated, the counter 22 is a corrugated member. That is to say ithas a number of undulations 22A or crests formed therein; adjacentundulations 22A or crests being separated by a valley 22B.

AS shown in FIG. 2 the temperature sensing means 32 is located in avalley 22B-between two adjacent undulations 22A. In FIG. 2 the invertedcup-like member 33, or.silicone rubber cup, is suitably bonded to theupper surface of the counter 22. Normally, as indicated in FIG. 2, theunstressed or uncompressed cup member 33 projects a short distance habove the top of an undulation 22A or crest. However, as shown in FIG. 3when a cooking vessel 38 is rested on the top surface of counter 22 andis supported by the undulations 22A thereof the cup 33 is compressed sothat the top of the cup 33 is substantially at the same height as anundulation 22A or crest. In other words, the dimension h (FIG..2) isreduced to zero.

Withv respect tothe spacing or frequency of undulations 22A andtheirarrangement in the counter 22, it is to be understood that many changeswill occur to those skilled in the art. For example, the undulations 22Aneed not be run in the direction indicated in the drawing figuresQTheundulations may run in a transverse direction. In the alternative, theundulations may be arranged in concentric circular patterns. Although inFIG. 3 the vessel 38 is illustrated as being supported by permeabilityfor magnetic flux. The coil 37 is, as shown, electrically coupled withthe thermistor unit 34 by the two electrical conductors 41. On theopposite side of the counter 22 (opposite valley 22B) there is mounted amagnetic receiving means which is designated generally by the referencenumber 60. As indicated in FIG. 5, the receiving means 60 is comprisedof a cylinder 61 which, advantageously, may be formed from the samematerials as cylinder 39 hereinbefore discussed. Embedded within thecylinder 61 is another magnetic core 62 about which there is wound acoil 63. Since the magnetic field intensity in the region where thetemperature sensing means 32, coupling means 35 and magnetic receivingmeans 60 are located is relatively low (i.e., in a region on an axisthrough the air core of induction coil relatively insignificant heatingcurrents will be induced in the means 32, 35 and 60. Moreover, thematerial of vessel 38 will constitute a low reluctance path for most ofthe magnetic flux produced by the coil 40.

Although the magnetic cores 36 and 62 are illustrated as being U-shapedcores, it is to be understood that cup-shaped cores may be employed toadvantage and such cores may have coils similar to the coils- 37 and 63appropriately disposed thereabout. Again, because of the maximumtemperatures experienced, the cylinder 61, like cylinder 39, may be madeof an epoxy, plastic, polyimide, etc.

Operationally, the temperature signal processing circuit 52 activelydrives the coil 63 electrically with ener- ,63 when so energizedfunctions in a manner similar to that of the primary winding of aconventional transformer. The voltage impressed across the coil 63causes current to flow through coil 63. This current flow is atfourundulations 22A, it is to be understood that more or 'less than fourundulations may be employed for this purpose.

5 The thermistor unit 34 is preferably partially embedded in theelastomeric cup member 33 as shown in FIG. 5 so thatat least one facethereof is available for tended by an electromagnetic field about coil63. Since the voltage impressed across the coil 63 is a changingvoltage, the current therethrough also changes as does the attendantmagnetic field. Consequently, a changing magnetic flux is introducedinto the magnetic core 62 of the receiving means 60. The magnetic fluxin the core 62 is coupled across the counter 22 to the magnetic core 36of the magnetic coupling means 35. The cores 36 and 62 form first andsecond magnetic flux paths and these flux paths together with thecounter 22 interposed therebetween form a magnetic circuit or loop. Thechanging magnetic flux in the core 36 induces a voltage across the coil37. Hence, the coil 37 functions in a manner similar to that of thesecondary winding of a conventional transformer. As indicated, thethermistor unit 34 is connected across the coil 37 by means of theconductors 41. Hence, the thermistor unit 34 acts as an electrical loadon the coil 37. As the vessel 38, which is in contact with thethermistor unit 34, is inductively heated by induction coil 40 heat istransferred to the thermistor unit 34 and the thermistor materialchanges the electrical resistance, or impedance, of the thermistor unitas a function of the temperature. In effect, there is connected acrossthe secondary winding or coil 37 a temperature-correlated resistiveload. In terms of transformer theory current flow in the coil 37 willproduce magnetic flux which reacts with the magnetic flux that isproduced by the coil 63, or primary winding. Thus, thetemperature-correlated resistive load represented by thermistor unit 34is reflected to the primary winding or coil 63. This reflectedresistance or impedance is related to the temperature of the vessel 38.The resistance or impedance reflected to the primary winding orcoil 63isemployed, in accordance with the invention, to develop or to modulatea signal in the temperature signal processing circuit 52 so as toprovide an output signal for driving the temperature indicator 30. Theaforementioned output signal delivered to temperature indicator 30 isrepresentative of the temperature of the vessel 38 as sensed, ordetected, by thermistor unit 34.

Advantageously, the temperature sensing unit employing the means andoperating in the manner hereinbefore described provides an inductionrange with the following features: the temperature sensing means 32 isan electrically passive device; the means 32 and 60 as well as theelements comprising these means need not withstand temperatures greaterthan 550 F andmay be fabricated from the materials hereinbeforediscussed; the relatively thin elastomer from which the cup-like member33 is formed exerts a relatively small restoring force against thebottom surface of the vessel 38 thereby eliminating the need for theprior art massive and complicated spring arrangements hereinbeforediscussed; being fabricated from a relatively thin elastomer such assilicone rubber, the cup-like member 33 easily contours itself to thebottom surfaces of ves-.

be wholly embedded in the cup-like member 33. In

suchcase although the thermistor unit or units 34 would not actuallycontact the vessel 38, the coupling is close enough so that the actualtemperature of vessel can be accurately detected.

I Illustrated at FIGS. 6 and 7 is an alternative temperature sensingmeans designated generally by the reference number 32A. With the systemshown at FIG. 6, however, the same magnetic receiving means 60 isemployed, The temperature sensing means 32A is as indicated at FIG. 6comprised of an elastomeric magnetic core 33A which resembles an openbladder. The core 33A includes two pole faces 33B and 33C which, asindicated,are separated by an air gap. Those portions of the core 33Awhich include the pole faces 33B and 33C are arranged on the counter 22in valley 228 so as to be opposite the corresponding pole faces of themagnetic core 62 of themagneticreceiving means 60. The properties of theelastomeric core 33A are discussed in detail hereinafter. Suffice it tosay at this point that the core 33A is fabricated from a material ormaterials which, in effect, have a magnetic permeability which is afunction of temperature. This relationship is graphically illustrated atFIG. 7. The core 33A is made from an elastomer so that it deforms in thesame manner as the cup-like member 33 (FIG. 5) and, in effect, has a lowrestoring force or spring constant so that it is easily deformed by avessel 38 resting thereupon.

operationally, changing current in the coil 63 of the receiving means 60produces a changing magnetic flux 4) which traverses the path or circuitshown in FIG. 6. For example, the magnetic flux (1) passes through thecore 62, through the counter 22 and through the elastic core 33A whereatit again passes through the counter 22 returning to the core 62. Thus,the flux qS traverses a closed magnetic path or loop. As indicated atFIG. 6, the air gap between the pole faces 33B and 33C should besufficiently large to prevent significant amounts of magnetic flux fromleaking thereacross and, in effect, short circuiting" the intended fluxpath through the core 33A. As the temperature of the vessel 38 increasesheat is transferred to the elastomeric core 33A. This activity issimilar to the activity hereinbefore described with respect to FIG. 3where heat from the pan 38 is transferred to the cup 33 and thermistor34. As the transferred heat increases the temperature of the core member33A, its magnetic permeability decreases in a manner similar to thatgraphically illustrated at FIG. 7. As a result, the coil 63 of thereceiving means 60 is, in

, effect, loaded, electrically. The effect is similar to that ofelectrically loadingthe secondary winding of a trans former so that theprimary winding thereof is loaded with a reflected impedance. Thiseffect is also similar to the action of a saturable reactor wherein aDC. winding controls the saturation level of a magnetic core and therebyloads an AC. drive winding disposed on the same core. Hence, thereflected impedance is employed to develop or to modulate a signal inthe temperature signal processing circuit 52 in the same manner ashereinbefore described with respect to the discussion relating to FIG.2.

As indicated in FIG. 6 the elastomeric magnetic core 33A may befabricated from a relatively thin piece of silicone rubber. Dispersedthroughout the silicone rubber, which serves as a matrix, is magneticmaterial in powder or small granular form. Such magnetic material may,for example, be ferrite powders, or granules, such as nickel-zincferrite, manganese-zinc ferrite or manganese-copper ferrite, amongothers. Such ferrite materials when embedded in the core member 33A willprovide a magnetic permeability versus temperature relationshipgenerally like that shown in the graph at FIG. 7. The ferrite materialsof the aforementioned nature are identified in published articles. Seefor example the article The Characteristics of Ferrite Cores with LowCurie Temperature and Their Application by K. Murakami, appearing in thepublication IEEE Transactions on Magnetics, 'June 1965 beginning at page96; Digital Magnetic Temperature Transducer by D.I. Tchernev et al.,appearing in the publication IEEE Transactions on Magnetics, Sept. 1971beginning at page 450. In the alternative, temperature sensitive firstorder transition materials may be dispersed in the silicone rubbermatrix 33A. For example, such transition materials as the following maybe employed: manganese arsenide (M,,A,), iron rhodill or chromium dopedmanganese antirnonide M,c,s,, See for example, the US. Pat. No.3,464,225 wherein the magnetic characteristics of such materials andtheir variation with temperature is discussed. See, also, thepublication Some Magnetic First Order Transitions, in the Journal ofApplied Physics, supplement to Vol. 33, No. 3, Mar. 1962 beginning atpage 1037.

Although the invention has been described and illustrated by way of aspecific embodiment with variations thereof, it is to be understood thatmany changes in details of construction and in the combination andarrangement of parts and components, as well as changes inconfigurations and materials, may be made without departing from thespirit and scope of the invention which is hereinafter claimed.

The valleys 22B between adjacent undulations 22A provide air gaps, orspaces, which are interposed between the heated bottom surface of thecooking vessel 38 and the surface of the counter 22, or vesselsupporting means. The air gaps, or spaces, provide a high thermalimpedance between the vessel 38 and counter 22 and thereby retard heatconduction therebetween to allow the vessel support surface of counter22 to remain relatively cool; i.e., at or near room temperature. Formore details see U.S. Pat. application of J. D.

' Harnden, Jr. and W. P. Komrumpf, Ser. No. 228,136,

filed 2/22/72, on even date herewith, titled Induction Cooking/WarmingAppliance Including Vessel Supporting Means With Irregular VesselSupport Surface (RD 5454) and assigned to the same assignee.

What is claimed is:.

1. An induction cooking/warming appliance, for heating a vessel havingat least one portion thereof in which heating current may be induced bysubjecting said one portion to a changing magnetic field, comprising:vessel supporting means in which no substantial heating current isinducted when said supporting means is subjected to a changing magneticfield, said supporting means having first and second back-to-backsurfaces, said first surface including at least two spacedapartundulations therein defining a valley therebetween, said vessel beingsupportable. on said two undulations; an induction coil energizable forproducing a changing magnetic field in said one portion of said vesselwhen said vessel is supported on said undulations; means for energizingsaid inductioncoil; temperature sensing means located in said valley andcomprising spring means, a temperature sensor unit supported by saidspring means and having an electrical impedance which varies withtemperature, means including a first magnetic flux path and a coil woundabout said first flux path and connected to said sensor unit, saidspring means being contacted and stressed by and second flux pathstogether with a portion of the interposed vessel supporting means form amagnetic circuit; and, means for electrically energizing said coil onsaid second magnetic flux path to introduce a changing magnetic fluxinto said magnetic circuit whereby the temperature variable impedance ofsaid sensor unit, as reflected to an electric circuit including saidcoil wound about said second flux path, is representative of thetemperature of said vessel.

2. The appliance according to claim 1 further comprising a temperaturesignal processing circuit and temperature indicator means, said signalprocessing circuit being electrically coupled to said coil wound aboutsaid second flux path and to said temperature indicator means wherebysaid signal processing circuit in response to said reflected impedanceproduces a signal representative of the temperature of said vessel forenergizing said indicator means whereby said temperature is visiblydisplayed.

3. The appliance according to claim 1 wherein said induction coil iselectrically energized with at least ultrasonic frequency and whereinsaid-coil on said second flux path is electrically energized at adifferent frequency.

4. The appliance according to claim 1 wherein said first surfaceincluding said undulations and valley present a relatively smoothsurface which is easily wiped clean.

5. The appliance according to claim 4 wherein said spring means is acup-like member of relatively thin elastic material having an exposedrelatively smooth surface which is easily wiped clean, said cup-likemember being secured in said valley and forming together with said firstsurface including said undulations and valley and enclosure for saidfirst flux path and coil thereabout, said sensor unit being at leastpartially embedded in said cup-like member, said cup-like member havinga relatively low restoring spring force.

6. The appliance according to claim 5 wherein said relatively thinelastic cup-like member of low restoring spring force is adapted forbeing contoured to the irregular surface of a vessel in contacttherewith.

7. An induction cooking/warming appliance, for heating a vessel havingat least one portion thereof in which heating current may be induced bysubjecting said one portion to a changing magnetic field, comprising:vessel supporting means in which no substantial heating current isinduced when said supporting means is subjected to a changing magneticfield, said supporting means having first and second back-to-backsurfaces, said first surface including at least two spacedapartundulations therein defining a valley therebetween, said vessel beingsupportable on said two undulations; an induction coil energizable forproducing a changing magnetic field in said one portion of the vesselwhen said vessel is supported on said undulations; means for energizingsaid induction coil; temperature sensing means, located in said valley,comprising means including a first magnetic flux path having a magneticpermeability which varies with temperature, said means including saidfirst flux path being contactable by said vessel when said vessel issupported on said two undulations; and, temperature receiving meanssupported on said second surface of said supporting means and locatedopposite said valley of said first surface whereby said vesselsupporting meansis interposed between said temperature sensing andreceiving means, said temperature receiving means comprising meansincluding a second magnetic flux path and a coil wound about said secondflux path whereby said first and second magnetic flux paths togetherwith a portion of the interposed vessel supporting means forms amagnetic circuit, the temperature variable magnetic permeability of saidfirst flux path causing said coil about said second flux path to becomeelectrically loaded with a reflected impedance representative of thetemperature of said vessel.

induction coil is electrically energized with at least ultrasonicfrequency and wherein said coil about said second flux path iselectrically energized at a different frequency.

10. The appliance according to claim 7 wherein said first surfaceincluding said undulations and valley present a relatively smoothsurface and is easily wiped clean.

11. The appliance according to claim 10 wherein said means includingfirst magnetic flux path is an open bladder member of relatively thinelastic material having an exposed relatively smooth surface which iseasily wiped clean.

12. The appliance according to claim 11 wherein said relatively thinelastic bladder member has a relatively low restoring spring force andis easily adapted for being contoured to the surface of an irregularlysurfaced vessel in contact therewith.

13. The appliance according to claim 7 wherein said means including saidfirst magnetic flux path is comprised offan elastomeric matrix inwhich'there is embedded powdered ferrite material, said matrix includ-14. The appliance according to claim 7 wherein said means including saidfirst magnetic flux path is comprised of an elastomeric matrix in whichthere is embedded powdered temperature sensitive first order transitionmaterial, said matrix and embedded powders having a magneticpermeability which varies with temperature.

15. The appliance according to claim 13 wherein said ferrite material isselected from the group consisting of nickel-zinc ferrite,manganese-zinc ferrite, and manganese-copper ferrite.

16. The appliance according to claim 14 wherein said first ordertransition material is selected from the group consisting of manganesearsenide, iron rhodium, and chromium doped manganese antimonide.

17. An induction cooking/warming appliance, for heating a vessel havingat least one portion thereof in which heating current may be induced bysubjecting said one portion to a changing magnetic fie d, comprising:Vessel supporting means in which no substantial heating current isinduced when said supporting means is subjected to a changing magneticfield, said supporting means having first and second surfaces, saidfirst surface including at least two spaced-apart undulations thereindefining a valley therebetween, said vessel being supportable on saidtwo undulations; an induction coil energizable for producing a changingmagnetic field in said one portion of said vessel when said vessel issupported on said undulations; means for energizing said induction coil;temperature sensing means located in said valley and including a firstmagnetic flux path; temperature receiving means supported on said secondsurface of said vessel supporting means and located opposite said valleyof said first surface whereby said vessel supporting means is interposedbetween said temperature sensing and receiving means, said temperaturereceiving means comprising a second magnetic flux path, said first andsecond flux paths together with a portion of the interposed vesselsupporting means forming a magnetic circuit; and means for introducing achanging magnetic flux into said magnetic circuit, the magnetic fluxintroduced into said magnetic circuit changing in response to thetemperature of said vessel; and means for deriving a signal in responseto the change of the magnetic flux in said magnetic circuit, said signalbeing representative of the temperature of said vessel.

1. An induction cooking/warming appliance, for heating a vessel havingat least one portion thereof in which heating current may be induced bysubjecting said one portion to a changing magnetic field, comprising:vessel supporting means in which no substantial heating current isinducted when said supporting means is subjected to a changing magneticfield, said supporting means having first and second back-to-backsurfaces, said first surface including at least two spaced-apartundulations therein defining a valley therebetween, said vessel beingsupportable on said two undulations; an induction coil energizable forproducing a changing magnetic field in said one portion of said vesselwhen said vessel is supported on said undulations; means for energizingsaid induction coil; temperature sensing means located in said valleyand comprising spring means, a temperature sensor unit supported by saidspring means and having an electrical impedance which varies withtemperature, means including a first magnetic flux path and a coil woundabout said first flux path and connected to said sensor unit, saidspring means being contacted and stressed by said vessel when saidvessel is supported on said two undulations and whereby said sensor unitsupported by said spring means is subjected to the temperature of saidvessel; temperature receiving means supported on said second surface ofsaid vessel supportiNg means and located opposite said valley of saidfirst surface whereby said vessel supporting means is interposed betweensaid temperature sensing and receiving means, said temperature receivingmeans comprising means including a second magnetic flux path and a coilwound about said second magnetic flux path whereby said first and secondflux paths together with a portion of the interposed vessel supportingmeans form a magnetic circuit; and, means for electrically energizingsaid coil on said second magnetic flux path to introduce a changingmagnetic flux into said magnetic circuit whereby the temperaturevariable impedance of said sensor unit, as reflected to an electriccircuit including said coil wound about said second flux path, isrepresentative of the temperature of said vessel.
 1. An inductioncooking/warming appliance, for heating a vessel having at least oneportion thereof in which heating current may be induced by subjectingsaid one portion to a changing magnetic field, comprising: vesselsupporting means in which no substantial heating current is inductedwhen said supporting means is subjected to a changing magnetic field,said supporting means having first and second back-to-back surfaces,said first surface including at least two spaced-apart undulationstherein defining a valley therebetween, said vessel being supportable onsaid two undulations; an induction coil energizable for producing achanging magnetic field in said one portion of said vessel when saidvessel is supported on said undulations; means for energizing saidinduction coil; temperature sensing means located in said valley andcomprising spring means, a temperature sensor unit supported by saidspring means and having an electrical impedance which varies withtemperature, means including a first magnetic flux path and a coil woundabout said first flux path and connected to said sensor unit, saidspring means being contacted and stressed by said vessel when saidvessel is supported on said two undulations and whereby said sensor unitsupported by said spring means is subjected to the temperature of saidvessel; temperature receiving means supported on said second surface ofsaid vessel supportiNg means and located opposite said valley of saidfirst surface whereby said vessel supporting means is interposed betweensaid temperature sensing and receiving means, said temperature receivingmeans comprising means including a second magnetic flux path and a coilwound about said second magnetic flux path whereby said first and secondflux paths together with a portion of the interposed vessel supportingmeans form a magnetic circuit; and, means for electrically energizingsaid coil on said second magnetic flux path to introduce a changingmagnetic flux into said magnetic circuit whereby the temperaturevariable impedance of said sensor unit, as reflected to an electriccircuit including said coil wound about said second flux path, isrepresentative of the temperature of said vessel.
 2. The applianceaccording to claim 1 further comprising a temperature signal processingcircuit and temperature indicator means, said signal processing circuitbeing electrically coupled to said coil wound about said second fluxpath and to said temperature indicator means whereby said signalprocessing circuit in response to said reflected impedance produces asignal representative of the temperature of said vessel for energizingsaid indicator means whereby said temperature is visibly displayed. 3.The appliance according to claim 1 wherein said induction coil iselectrically energized with at least ultrasonic frequency and whereinsaid coil on said second flux path is electrically energized at adifferent frequency.
 4. The appliance according to claim 1 wherein saidfirst surface including said undulations and valley present a relativelysmooth surface which is easily wiped clean.
 5. The appliance accordingto claim 4 wherein said spring means is a cup-like member of relativelythin elastic material having an exposed relatively smooth surface whichis easily wiped clean, said cup-like member being secured in said valleyand forming together with said first surface including said undulationsand valley and enclosure for said first flux path and coil thereabout,said sensor unit being at least partially embedded in said cup-likemember, said cup-like member having a relatively low restoring springforce.
 6. The appliance according to claim 5 wherein said relativelythin elastic cup-like member of low restoring spring force is adaptedfor being contoured to the irregular surface of a vessel in contacttherewith.
 7. An induction cooking/warming appliance, for heating avessel having at least one portion thereof in which heating current maybe induced by subjecting said one portion to a changing magnetic field,comprising: vessel supporting means in which no substantial heatingcurrent is induced when said supporting means is subjected to a changingmagnetic field, said supporting means having first and secondback-to-back surfaces, said first surface including at least twospaced-apart undulations therein defining a valley therebetween, saidvessel being supportable on said two undulations; an induction coilenergizable for producing a changing magnetic field in said one portionof the vessel when said vessel is supported on said undulations; meansfor energizing said induction coil; temperature sensing means, locatedin said valley, comprising means including a first magnetic flux pathhaving a magnetic permeability which varies with temperature, said meansincluding said first flux path being contactable by said vessel whensaid vessel is supported on said two undulations; and, temperaturereceiving means supported on said second surface of said supportingmeans and located opposite said valley of said first surface wherebysaid vessel supporting means is interposed between said temperaturesensing and receiving means, said temperature receiving means comprisingmeans including a second magnetic flux path and a coil wound about saidsecond flux path whereby said first and second magnetic flux pathstogether with a portion of the interposed vessel supporting means formsa Magnetic circuit, the temperature variable magnetic permeability ofsaid first flux path causing said coil about said second flux path tobecome electrically loaded with a reflected impedance representative ofthe temperature of said vessel.
 8. The appliance according to claim 7further comprising a temperature signal processing circuit andtemperature indicator means, said signal processing circuit beingelectrically connected to said coil wound about said second flux pathand connected to said temperature indicator means whereby said signalprocessing circuit in response to said reflected impedance produces asignal representative of the temperature of said vessel for energizingsaid indicator means whereby said temperature is visibly displayed. 9.The appliance according to claim 7 wherein said induction coil iselectrically energized with at least ultrasonic frequency and whereinsaid coil about said second flux path is electrically energized at adifferent frequency.
 10. The appliance according to claim 7 wherein saidfirst surface including said undulations and valley present a relativelysmooth surface and is easily wiped clean.
 11. The appliance according toclaim 10 wherein said means including first magnetic flux path is anopen bladder member of relatively thin elastic material having anexposed relatively smooth surface which is easily wiped clean.
 12. Theappliance according to claim 11 wherein said relatively thin elasticbladder member has a relatively low restoring spring force and is easilyadapted for being contoured to the surface of an irregularly surfacedvessel in contact therewith.
 13. The appliance according to claim 7wherein said means including said first magnetic flux path is comprisedof an elastomeric matrix in which there is embedded powdered ferritematerial, said matrix including said embedded ferrite powder having amagnetic permeability which varies with temperature.
 14. The applianceaccording to claim 7 wherein said means including said first magneticflux path is comprised of an elastomeric matrix in which there isembedded powdered temperature sensitive first order transition material,said matrix and embedded powders having a magnetic permeability whichvaries with temperature.
 15. The appliance according to claim 13 whereinsaid ferrite material is selected from the group consisting ofnickel-zinc ferrite, manganese-zinc ferrite, and manganese-copperferrite.
 16. The appliance according to claim 14 wherein said firstorder transition material is selected from the group consisting ofmanganese arsenide, iron rhodium, and chromium doped manganeseantimonide.